Halogenated phenacylpyridines and process of preparing the same



Patented Jan. 14, 1947 HALOGENATED PHENA INESAND CYLPYBID PROCESS OF PREPARING THE SAME James M. Smith, Jr.,

signor to American C North Plainfleld, N. 3., as-

yanamid Company, New

York, N. Y., a corporation of Maine No Drawing. Application June Serial No. 598,626

11 Claims. (01. 260-295) This invention relates to new organic compounds and to methods of preparing the same.

The new compounds of the present invention may be illustrated by the following general form a:

in which X is a halogen, R isv a member of the group consisting of pyridine, benzopyridine and alkyl pyridine radicals, and R is an aryl radical. The compounds are characterized as being crystalline solids, substantially insoluble in water and diflicultly soluble in inert organic solvents. These new compounds are useful as intermediates in the preparation of analgesics and other useful organic compounds, some having properties.

Compounds having the above formula may be 7 prepared by treating a phenacylpyridine with a halogen, such as bromine or chlorine, while sus pended or dissolved in a suitable organic liquid at temperatures of from about C. to 100 C., preferably between and 50 C. The resulting w-halophenacyipyridine may be used directly or it may be isolated by precipitation upon dilution of the solvent with water or by evaporation of the solvent, as illustrated in the specific examples.

Among the phenacylpyridines which may be halogenated in accordance with the process of the present invention are such phenacylpyridines as Z-phenacylpyridine, 4-phenacylpyrldine, 2- phenacyl-5,6-benzopyridine, 4-phenacyl-5,6-benzopyridine, 2 methyl 6 phenacylpyridine, 4- methyl 2 phenacylpyridine, 4,6-dimethyl 2 phenacylpyridine, 2-methyl-5-ethyl-6-phenacylpyridine, and other phenacylpyridines having alkyl and alkylene substituents on the pyridine ring. The aryl radical, R, may have one or more substituent radicals, such as chlorine, bromine, methyl, methoxy, nitro carbethoxy, and the like.

To properly halogenate the phenacylpyridine I use a substantially equimolar proportion of the halogen; that is. about two equivalents of halogen for each mole of thephenacylpyridine. If a large excess of halogenating agent is used, for example, more than 10% of the theoretical requirements, the yield of pure product is greatly reduced.

As solvents for the reaction there may be used glacial acetic acid, trichlorethylene, ethylene dichloride, diethyl ether, dibutyl ether, chloroform, carbon disulfide, and other organic liquids which are substantially inert to bromine. under conditions of the reaction. In general, the presence therapeutic 2 drolysis with resulting splitting of the phenacylpyridine. or the various solvents, I greatly prefer to use .glacial acetic acid although ether is preferred when halogenating 2-phenacylbenzopyridine.

Although the reaction proceeds rapidly and reaches a substantial degree of completion within a few minutes, particularly when using chlorine at room temperature, it may be advisable, and will do no harm, to allow the reactants to remain in contact for several hours. I

The invention will be illustrated in greater detail by means of the following specific examples in which representative phenacylpyridines are halogenated under different conditions to produce the new compounds of the present invention. It is to be understood that these examples are intended to illustrate the invention and are not in limitation thereof since, obviously, certain changes may be made therein by those skilled in the art.

Example 1 A solution of 22.4 g. z-phenacylpyridine (Scheuing and Winterhalder to Boehringer and Sohn,

D. R. P. 594,849, 3/22/34; Friedl. 19, 1147) in 200 cc. glacial acetic acid at. C.'i's treated with a slight excess of the theoretical two equivalents of bromine dissolved in 200 cc. glacial acetic acid, added over a period of about one hour. The tem- Derature is maintained at 90-100 C. for about one hour longer, then the solution is cooled to room temperature and allowed to stand overnight. The next day cc. of solvent is distilled off. On dilution of the residual solution with ice and water, the 2-(w-bromophenacyl) pyridine precipitates and is isolated by filtration. The new compound may be purified by dissolving in acetic acid, treating with activated charcoal, filtering, and diluting the filtrate with ice. It melts at 93-94 C.

Example 2 dine may be dried as is: or preferably the cake of water is to be avoided as it tends to cause hy- 55 is wetted with a volatile solvent such as hexane or isopropyl ether, sucked as dry as possible on the filter, and then dried at about 50 C. to constant weight. The yield of 2- (u-bromophenacyl) g. more 2-(u-bromophenacyl)pyridine, melting point 91-93 C.

Example 3 To a solution of 98.6 g. of 4-phenacylpyridine (A. E. Tchitchibabin, Rec. Trav. 'Chlm. 57, 582-5 (1938)) in 375 cc. of'glacial. acetic-acid at room I temperature there is added rapidly with vigorous stirring a solution of 79.9 g. of bromine in 125 cc. of glacial acetic acid. The temperature rises to 55 C. and'crystals begin to form almost immediately. After standing for 45 minutes the light grey crystals of 4-(w-bromophenacyllpyridine hydrobromide are isolated by filtration, glacial acetic acid is removed by washing with mixed hexanes and the product is dried at 50 C. The yield of 4-(w-bromophenacyl) pyridine hydrobromide is 178.5 g. representing 100% of the theory; the melting point is about 221 C. (deeomp.). It may be crystallized from glacial acetic acid. It is stable if kept in a tightly stoppered bottle but decomposes rapidly on exposure to moisture.

Example 4 droxide in 800 cc. hot alcohol gives 22 g. phenyl- -4-quinolylacetylene; boiling point 205-210 C.

at 3 mm.

A solution of 15 g. pheny1-4-quinglylacetylene in 1000 cc. 65% sulfuric acid is boiled five minutes. On cooling, dilution, and neutralization with ammonia there is obtained 16 g. 4-phenacylquinoline; melting point about 114 C.

' A solution of 10 g. 4-phenacylquinoline in 100 cc. glacial aceticacid is treated with a slight excess of the theoretical amount of bromine in 25 cc. glacial acetic acid, which is added at 20-25 C. in about fifteen minutes. After standing at room temperature for several hours,.the solution is treated with a little activated charcoal and filtered. The filtrate is diluted with water to about 1 liter of solution, and the precipitate is collected on the filter. It is then washed with water, wet with a volatile solvent such as mixed hexanes, or isopropylacetate, and dried at about 50 C. The yield of 4-(w-bromophenacyl)-5,65

benzopyridine is 10 g.; melting point about 115-120C:

Example 5 50 g. of 2-phenacylquinoline (Scheuing and Winterhalder to Boehringer and Sohn, D. R. P. 594,849, 3/22/34; Friedl. 19, 1147) in 1500 cc. anhydrous ether with 20 g. powdered calcium carbonate is treated with 32 g. bromine in 500 cc.

Example 6 100 parts by weight or 4-pyrophthalone (see Ber. 38. 161 (1905)) is added to 1225 parts of "water and the slurry dissolved by the addition of one equivalent weight of 5 N sodium hydroxlde. The red solution is heated to -90 C. and 79 parts by weight of diethyl sulfate. is gradually added. A yellow precipitate rapidly appears. The mixture is heated after the addition of the ethylating agent for a time suflicient to complete the reaction. The reaction mixture is cooled, and the product removed by filtration. The light yellow crystals are washed thoroughly with water and dried. The yield of 4-(o-carbethoxyphenacyhpyridine is about parts by weight. The melt P int is 253.7 to 256.7 C.

To parts by weight of glacial acetic acid is added 100 parts by weigh-t of 4-(o-carbethoxyphenacyl) pyridine. To the solution at approximately room temperature is added 63 parts by weight of bromine. A yellow precipitate rapidly appears. This is the hydrobromide of the product, 4- (w-bromo-o-carbethoxyphenacyl) pyridine. After the addition is complete. the slurry is stirred for a short time and then the solid removed by filtration. The solid is washed thoroughly with an organic solvent to remove the acetic acid. It is then dried. The yield is about 50 parts by weight but more material may be obtained in the mother liquor. The melting point, with decomposition, is 225.5" C.

Example 7 in which X is a halogen. R is a member of the group consisting of pyridine, benzopyridine and alkylpyridine radicals, and R is an aryl radical. 2. Compounds having the general formula in which R is a pyridine radical.

3. 2- (w-bromophenacyl) pyridine. -4. 4-(w-bromophenacyl) pyridine. 5. w-bromo-4-phenacyl-5,6-benzopyridine. 6. A method of preparing compounds having the general formula in which X is a halogen. R. is a member of the group consisting of pyridine, benzopyridine and alkylpyridine radicals, and R is an aryl radical which comprises the steps of suspending a phenacylpyridine in an inert organic liquid with a halogen at a temperature of about 10 C. 'to 100 C.

' alkylpyridine radicals,

- the general formula 5 7. A method or preparing compounds having the general formula halogen at a temperature of about 10 C. to 100 C.

8. A method oi preparing compounds having in which R is a pyridine radical and R. is an aryl radical which comprises the steps of suspending a phenacylpyridine in glacial acetic acid with v 6 bromine at a temperature within the range 10 C. to 100 C.

9; A method of preparing 2-(u-bromophenacyl) pyridine which comprises suspending 2- phenacylpyridine in glacial acetic acid with bromine at a temperature within to '100 C.

t 10. A method of preparing 4-(u-bromophenacyDpyridine which comprises suspending 4- phenacylpyridine in glacial acetic acid with bromine at a temperature within the range 10 C to 11. A method of preparing i-(w-bromophenacyl)-5,6-benzopyridine which comprises suspending 4-phenaqyl-5fi-benzopyridine in glacial acetic acid with bromine at a temperature within the range 10 to100 C;

' JAMES M. SMITH, JR.

the range 10 C. 

